Storage of a liquefied gas

ABSTRACT

947,851. Carrying liquefied gases. CONCH INTERNATIONAL METHANE Ltd. Nov. 6, 1962, No. 41989/62. Heading B7A. [Also in Division F4] A prismatic liquefied gas container 10, Fig. 1, is located within a plywood facing 9 of balsa wood blocks 8 lining a liquid-tight housing 7 within the inner hull 3 of a ship 1 by engagement of spaced keys 19, Fig. 2, welded to the outer edges of a framework 11 of the container, (see Division F4) with wooden blocks 23, Fig. 4 slidably mounted between jaws of clamps 21 bolted to blocks 22 secured along the corner edges of the facing 9 and the blocks are adjustably positioned against the action of leaf springs 20 welded to the frame 11 by cam rods 24 which extend through the surrounding insulation and whereby during filling the tank frame 11 is held in abutment with said blocks 23.

Dec. 21, 1965 M. J. FRENCH 3,224,624

STORAGE OF A LIQUEFIED GAS Filed Aug. 20, 1963 4 Sheets-Sheet 1 Inventor Ml chae/ BJ Hench Attorney Dec. 21, 1965 M. J. FRENCH 3,224,624

STORAGE OF A LIQUEFIED GAS Filed Aug. 20, 1963 4 Sheets-Sheet 2 Inventor M/chge/ J 56n y 4 Atmmey Dec. 21, 1965 M. J. FRENCH 3,224,624

STORAGE OF A LIQUEFIED GAS 4 Sheets-Sheet 4 Filed Aug. 20, 1963 United States Patent 3,224,624 STQRAGE F A LKQUEFIED GAS Michael Joseph French, Cambridge, England, assignor to (lunch International Methane Limited, Nassau, Ballamas, a Bahamian company Filed Aug. 20, 1963, Ser. No. 303,290 Claims priority, application Great Britain, Nov. 6, 1962, 41,989/ 62 7 Claims. (Ci. 22tl15) This invention concerns improvements in or relating to the storage of a liquefied gas. More particularly, it concerns a tank for the storage of a liquefied gas. By liquefied gas it is means liquid that boils at atmospheric pressure and at a temperature below the ambient temperature, for example natural gas (which consist-s mainly of methane), propane, hydrogen, nitrogen or oxygen.

A liquefied gas can be stored in a tank having metal walls secured to a rigid framework and externally supported by thermal insulation, the tank and the insulation being located in a rigid structure, for example the hull of a ship. However, the construction and use of such a tank offers difiiculties, because when the tank is being charged with a liquefied gas, the resultant drop in temperature of the material of the tank will cause the tank to contract. This contraction can cause the walls of the tank to draw back from the supporting insulation. Moreover, the contraction can cause the walls of the tank to tear away from the rigid framework to which they are secured, owing to differences between the amounts by which the framework and the walls may contract.

According to the invention, a tank for the storage of a liquefied gas is one in which at least one of the walls comprises a rigid framework defining at least one wall space; a separate metal sheet for covering each wall space; metal bellows for securing each metal sheet to the framework so that the whole wall is impervious to liquid; and in the upper region of each sheet at least one strap secured to the sheet and the adjacent framework.

By these means a tank can be obtained in which the walls of the tank are prevented from contracting away from external supporting insulation. In a tank according to the invention, each metal sheet secured to a rigid framework by a metal bellows is free to contract or expand in area relatively to the framework when the tank is being charged or discharged. Thus, when the tank is being charged, each metal bellows accommodates strains produced in the walls of the tank by the difference in contraction of the rigid framework and the metal sheet or sheets thereby preventing the metal sheet or sheets from tearing away from the framework. A tank according to the invention can be used for the storage of liquid at or about atmospheric pressure, particularly a liquefied gas.

The metal sheet or sheets to be secured to any of the rigid frameworks can be of any thickness appropriate to the stresses to be taken by them, but they can be so thin and of so little strength that they are not self supporting, that is they are membranes. They are impervious to the contents of the tank and are preferably made from metals that retain a high degree of ductility and strength at the low temperatures to be encountered by the tank. Preferably, the metal sheets are made from aluminium, alloys of aluminium, stainless steels or nickel steels.

The rigid framework of a wall of a tank according to the invention provides the skeleton of the tank, and can enclose at least one wall space to be covered to form a wall of the tank. The periphery of the framework lies along edges of the tank, which can be located and supported in a surrounding structure by way of suitable spacers. Individual members of the framework can be 3,224,624 Patented Dec. 21, 1965 of any size and shape for giving adequate strength and rigidity to the walls of the tank. The members of the framework can be made from any suitable material, for example wood, plastic laminates or metal. Preferably, the members of the framework are of the same material as the metal sheet or sheets, for example stainless steel.

The metal bellows for securing a metal sheet especially the periphery of the sheet, to a rigid framework can have at least one convolution. A preferred bellows is one having a single convolution, which is provided with a flange for securing the bellows to the rigid framework. The thickness of the material of the bellows is at least as thick as that of the metal sheet to be joined to one end of the bellows, but is preferably the same thickness. The bellows is preferably made from the same metal as that used for the metal sheet or sheets to be secured to the rigid framework, for example aluminium, alloys of aluminium, stainless steels or nickel steels. In fitting the bellows, it is preferred first to join one end of the bellows to the rigid framework and then stress the bellows fully at the minimum satisfactory radius before joining the metal sheet to the other end of the bellows so as to prestress the bellows in such a way that when the tank is filled the prestress will be relieved or reversed.

The straps are used to prevent the sheets creeping downwards due to the differences between the hydrostatic pressure at the top and bottom parts of the bellows when the tank is charged with a liquefied gas, and they also preent shear buckling of the sheets in the unloaded state.

They may be of the same metal as the metal sheet or bellows. Preferably the tank comprises more than one strap spaced at regular intervals along the sheet and framework.

In the construction of a tank for the storage of a liquefied gas in which all of the walls of the tank are fabricated from rigid metal frameworks, metal sheets and metal bellows, the walls can be fabricated by locating and supporting the members of the frameworks in a rigid structure, and then welding together the framework members. After they have been heavily loaded in tension, the metal bellows and then the metal sheets can be welded into place. Alternatively, the walls of the tank can be constructed from suitable prefabricated panels prestressed as described above individually comprising a rigid framework, at least one metal sheet and at least one metal bellows. The panels are located and supported in the rigid structure and are then Welded together at the frameworks of the panels.

Thermal insulation for supporting the walls of a tank according to the invention encloses a space for containing the tank, the inner face of the insulation conforming with the shape of the outside of the tank and preferably maintaining its shape during repeated temperature changes. The insulation can be in the form of sheets, granulated material or powder. The insulation can be any suitable thermal insulation, for example asbestos, balsa wood faced with plywood, diatomaceous earth, foamed glass, foamed elastomeric material for instance polystyrene or polyurethane foam, glass wool, granulated cork, mineral wool,

paper honeycomb or pearlite. Preferably, the insulation is a material that when in position neither substantially con-tracts nor substantially expands during changes in its temperature, for example balsa wood faced with plywood.

It is prudent (and in the case of sea going vessel for the transport of a liquefied gas a classification requirement) to surround the tank with a safety barrier for containing any cold liquid and gas that might escape from the tank. This barrier can be constituted by the thermal insulation for the tank or by an impervious material thermally insulated from the external rigid structure. The impervious material can be in the form of an impervious facing (for example a layer of metal, plastic or plywood) on the outer face of the thermal insulation for the tank or in the form of an outer tank containing the cargo tank and its thermal insulation. The cargo tank, thermal insulation and the safety barrier can be contained in a suitable housing (for example a plywood or aluminium housing), which can constitute a further safety barrier. If this composite tank is to be located in the hold of a ship, it is preferably supported by suitable spacers connected to the structure of the ship, so that stresses in the walls of the cargo tank are transmitted to the structure of the ship. These spaces can be constituted by load bearing thermal insulation, for example wooden beams. Any space between the housing and the hull of the ship is preferably filled with a thermally insulating material, which can be the same as that used to support the walls of the cargo tank. The total amount of thermal insulation used in the composite tank and to fill any space between the housing and the hull of the ship should be sutficient to keep the temperature of the hull above the embrittlement temperature of the material of the hull when a liquefied gas is charged into the tank. This requirement is of particular concern when the cargo tank contains liquefied natural gas, which boils at atmospheric pressure at a temperature of about minus 258 F.

The invention will now be further described with reference to the accompanying drawings in which:

FIGURE 1 is a schematic elevation of a part of a ship comprising a tank for the transport of a liquefied gas;

FIGURE 2 is an elevation of a wall of the tank shown in FIGURE 1 in which part of the wall is broken away;

FIGURE 3 is an elevation looking at a vertical edge of the tank shown in FIGURE 1;

FIGURE 4 is a sectional elevation showing how a horizontal edge of the tank shown in FIGURE 1 is located; and

FIGURE 5 is a fragmentary elevation of a wall of a modification of the tank shaown in FIGURE 1.

FIGURE 6 shows an alternative form of tank construction;

FIGURE 7 is a perspective view, partly broken away, showing the tank framework in place with one sheet assembled.

In FIGURE 1, a ship 1 has an outer hull 2 and an inner hull 3 inwardly spaced therefrom, both hulls being fabricated from steel plates. Ballast water can be kept in space 4 between the hulls. Inwardly spaced from the inner hull and separated therefrom by wooden spacers 5 and blocks 6 of polyurethane foam is a liquid tight plywood housing 7. Immediately within the housing are balsa wood blocks 8 provided with facings 9 of plywood on their inner faces. These blocks enclose a space for a prismatic tank 10 for the transport of a liquefied gas. When the tank is charged or being charged with a liquefied gas, the walls of the tank are in sliding oontact with facings 9.

In FIGURE 2, there is shown a wall of tank 10 with some of the fittings used to locate and support the tank in housing 7. The walls not shown are similar. Each wall of the tank comprises a rigid framework 11 of stainless steel beams inwardly sloping and welded together at mitre joints. Each framework 11 defines a wall space that is covered by a non-self-supporting sheet 12 of stainless steel. The periphery of each sheet 12 is welded to one edge of a stainless steel bellows 13 having a single convolution (see FIGURE 4). Each bellows 13 is fabricated from a longitudinal half section of a stainless steel cylinder. The half section is bent to provide the corners for the bellows. The ends of the half section are then welded together, the weld 14 lying at a plane along one of the straight sides of the resultant bellows. Welds 14 were heat treated and rolled to make them flexible. The other edge of each bellows 13 is welded to an edge of a stainless steel flange 15. The other edge of each flange 15 is sealed and welded to a wall of a slot 16 provided in the innermost face of the part of framework 11 surrounding the hole covered by sheet 12 (see FIG- URE 4). Alternatively, the other end of each flange 15 could have been sealed and secured in a slot 16 by adhesive bonding. Each flange 15 is fabricated from four sections, welded together so that the welds 17 lie at the corners of the framework. Welds 17 were heat treated and rolled to make them flexible. Welded to the outside of the upper parts of frameworks 11 and to the outside of the upper parts of sheets 12 are straps in the form of stainless steel hangers 18. Welded to the outside of the parts of frameworks 11 forming the vertical and horizontal edges of the tank are stainless steel keys 19 (only one vertical edge and one horizontal edge so treated are shown in FIGURE 2). Each key 19 comprises a rectangular stainless steel block welded along one of its long sides to the outside of framework 11. Stainless steel leaf springs 20 are welded to the outside of frameworks 11 between adjacent keys 19 (only one part of a framework 11 so treated is shown in FIGURE 3). Each leaf spring 20 comprises two arms diverging from a stem, which is welded to the outside of a framework 11. Keys 19 and springs 20 are used to locate the tank in housing 9 as described below.

In FIGURE 4, the manner in which a horizontal part of a framework 11 is located in housing 7 is shown in detail. Keys 19 welded to the outside of a horizontal part of a framework 11 enter clamps 21 (which are like clamps for securing railway lines to sleepers) bolted via wooden blocks 22 into the inside of an edge of housing 9 formed by the intersection of two walls of the housing. Within the jaws of each clamp 21, a key 19 rests on block 23 seated on a flat of a rod 24 provided with flats 25 along its length. These rods 24 may also if desired have raised portions of greater radial dimensions. Two rods 24 are provided for the whole length of the edge of the tank so that each rod deals with half of the length of the edge. The other horizontal and the vertical parts of frameworks 11 are similarly treated, except that a single rod 24- extending down the whole of the length of the outside of each vertical part is used.

The arms of each leaf spring 20 welded to the outside of a horizontal edge of framework 11 are bolted to the two facings 9 to which are secured clamps 21, each arm being attached to not more than one facing. The springs ensure that when tank 10 (and hence framework 11) contracts as a result of it being charged with a liquefied gas, the tank contracts towards its centre.

The outer ends of rods 24 in the case of the horizontal edges of tank 10 and the upper ends of rods 24 in the case of the vertical edges of tank 10 pass through facings 9, blocks and housing 7 via glands. When rods 24 are actuated, i.e., turned, moved axially or both, by bell cranks fitted to their ends outside housing 7 and connected by rods to a suitable motor on the ship, the flats on rods 24 provide cam edges for urging block 23 outwardly in the jaws of clamps 21. When the tank is being charged with liquefied gas, suitable rotation of rods 24 keeps blocks 23 in contact with keys 19 and enables the resultant contraction of the tank away from housing 7 to be compensated for, thereby ensuring that the tank is rigidly located and supported in housing 7.

In FIGURE 5, there is shown a fragment of a wall 30 of a modification of tank 10 described with reference to FIGURES 2 to 4. Wall 30 comprises a stainless steel framework 31 defining a plurality of wall spaces covered by nonself-supporting stainless steel sheets 32. Sheets 32 are secured to framewark 31 in the same way as sheets 12 are secured to framework 11 of tank 10 described with reference to FIGURES 2 to 4.

As an alternative to the above described tank which requires the use of rods and leaf springs for all the wall frameworks of the tank, a tank may be made in which the bottom comprises a thick sheet or plate. When the tank is used in the hold of a ship, for the storage of a liquefied gas, it should be able to expand and contract, and yet be stable against the displacement forces arising from the pitching and rolling movements of the ship. Accordingly, with such a tank it is preferable if there is a key and keyway arrangement between the bottom of the tank and the adjacent insulation, and also preferably a similar arrangement at the top of the tank.

A vertical cross-section of such a tank, and the inner part of the insulated housing is shown in FIGURE 6 of the drawings.

Numerals 9 to 13 indicate the same parts that are described with reference to FIGURES 1 to 4 of the drawings. The bottom of the tank consists of a thick sheet or plate 41. At the bottom centre of this sheet a key 42 is secured. This key is held within the keyway 43 formed by plywood facing 9 within the balsa wood blocks 8.

The top of the tank consists of the membrane/ bellows combination described above, but in order that a key and keyway may be attached, there are two membranes. The frameworks 11 are attached to the top key 44 which is in the centre of the top wall. This key 44 engages a keyway 45 constructed similarly to the bottom keyway 43.

With this form of tank there is no need for any rods 24, clamps 21 or leaf springs 20. When the tank contracts the side walls and top contract inwardly and the bottom 41 contracts towards its centre, there being relative sliding movement between the metal bottom 41 and the plywood facing 9. The top and bottom key and keyways ensures that the tank is stable in position.

Another possible alternative type of tank is as follows. The top and bottom Walls of the tank each have at least two membranes attached by bellows to a framework. Both the top and bottom walls are bisected by the framework. Keys and keyways are fixed at the centres of the top and bottom walls in a manner similar to that described with reference to FIGURE 6. The only places where load-bearing rods 24 and leaf springs are required is on the top wall along the edges perpendicular to the top key and keyway. Also in order to take the weight of the tank when it shrinks, there should be rods 24 round the edges of the bottom wall.

I claim:

l. A prismatic tank for the low-temperature storage of liquefied gas at atmospheric pressure comprising (a) a rigid prismatic insulating outer container having interior wall surfaces defining generally the interior of the tank,

(b) an inner container comprising at least one impervious, semi rigid metal membrane sheet immediately adjacent each said wall surface,

(c) a rigid framework outlining each said wall surface, with the framework members lying exteriorly of said inner container in the angles formed by adjacent wall surfaces,

(cl) a metal bellows securing at least some of said sheets to said framework in liquid-tight fashion so that the entire inner containers is liquid-tight, while permitting limited relative movement between the tank and framework,

(e) and cooperating restraining means between said framework and said outer container supporting said framework on said outer container, independently of the metal bellows, in such a manner as to permit limited thermal contraction of the framework within the container.

2. A tank as claimed in claim 1, said metal bellows comprising a single convolution provided with a flange for securing the bellows to the rigid framework.

3. A tank as claimed in claim 1 in which the bottom wall comprises a thick sheet, the tank is contained in a thermally insulated housing, and in which there are cooperating keys and keyways between the framework of the top wall of the tank and thermal insulation of the tank housing and between the bottom wall of the tank and thermal insulation of the tank housing.

4. A tank as claimed in claim 1, including a metal bellows securing the top edge of a sidewall sheet to the adjacent framework, and at least one strap securing the same adjacent framework element to the same sheet at a region below the bellows.

5. A tank as claimed in claim 4, including a plurality of such straps for each sheet, the straps being spaced at regular intervals along the top part of the sheet.

6. A container for the storage of a liquefied gas, comprising an outer housing and a tank within said housing, a rigid framework defining the perimeter of at least one wall space of the tank; a separate metal sheet placed inwardly of the framework for covering each wall space defined by the framework; metal bellows for securing each metal sheet to the framework so that the whole wall is impervious to liquid; a resilient framework supporting device fixed to the outer housing and biased to urge the framework inwardly toward the tank center when the tank contracts, and supporting the framework independently of said bellows; near each edge of each sheet covering a top wall space at least one strap secured to the sheet and t0 the adjacent framework, and in the upper region of each sheet covering a side wall space, at least one strap secured to the sheet and to the adjacent framework.

7. A container as claimed in claim 6, in which the framework supporting device comprises clamps fixed to the outer housing, keys attached to the outer edges of the framework and seated in said clamps, rods having cam sections passing through said clamps, which cam sect-ions co-operate with said keys, means for operating said cam sections against the keys, and leaf springs attached to the outer housing and outer edges of the framework so as to urge the framework inwardly towards the tank center.

References Cited by the Examiner UNITED STATES PATENTS 2,861,707 11/1958 Moorman 22015 2,944,692 7/1960 Farrell et al. 2209 2,944,693 7/1960 Benson et al 2209 2,954,003 9/1960 Farrell et al. 220-15 2,994,452 8/1961 Morrison 2209 3,085,708 4/1963 Dosker 220-9 FOREIGN PATENTS 1,249,510 11/1960 France.

898,267 6/1962 Great Britain.

THERON E. CONDON, Primary Examiner. 

1. A PRISMATIC TANK FOR THE LOW-TEMPERATURE STORAGE OF LIQUEFIED GAS AT ATMOSPHERIC PRESSURE COMPRISING (A) A RIGID PRISMATIC INSULATING OUTER CONTAINER HAVING INTERIOR WALL SURFACES DEFINING GENERALLY THE INTERIOR OF THE TANK, (B) AN INNER CONTAINER COMPRISING AT LEAST ONE IMPERVIOUS, SEMI-RIGID METAL MEMBRANE SHEET IMMEDIATELY ADJACENT EACH SAID WALL SURFACE, (C) A RIGID FRAMEWORK OUTLING EACH SAID WALL SURFACE, WITH THE FRAMEWORK MEMBERS LYING EXTERIORLY OF SAID INNER CONTAINER IN THE ANGLES FORMED BY ADJACENT WALL SURFACES, (D) A METAL BELLOWS SECURING AT LEAST SOME OF SAID SHEETS TO SAID FRAMEWORK IN LIQUID-TIGHT FASHION SO THAT THE ENTIRE INNER CONTAINERS IN LIQUID-TIGHT, WHILE PERMITTING LIMITED RELATIVE MOVEMENT BETWEEN THE TANK AND FRAMEWORK, (E) AND COOPERATING RESTRAINING MEANS BETWEEN SAID FRAMEWORK AND SAID OUTER CONTAINER SUPPORTING SAID FRAMEWORK ON SAID OUTER CONTAINER, INDEPENDENTLY OF THE METAL BELLOWS, IN SUCH A MANNER AS TO PERMIT LIMITED THERMAL CONTRACTION OF THE FRAMEWORK WITHIN THE CONTAINER. 